Printing devices are essential information apparatuses in modern offices. The printing devices include for example copiers, printers, scanners and multifunction peripherals. Among these printing devices, printers are the most popular. Generally, after a printer is connected to a computer, the document file of the computer could be printed on many kinds of media (e.g. blank papers).
FIG. 1 is a schematic perspective view illustrating an inkjet printer according to the prior art. As shown in FIG. 1, the inkjet printer 1 comprises an ink cartridge 10, plural ink nozzles (not shown), a transmission mechanism 11, a sheet input tray 12 and a sheet output tray 13. The ink cartridge 10 is used for storing ink. The ink nozzles are used for ejecting ink. The ink nozzles are disposed at the bottom of the transmission mechanism 11. The transmission mechanism 11 is used for moving the ink nozzles, so that the ink could be ejected through the ink nozzles of inkjet printer 1 and printed on any position of a blank paper P. The sheet input tray 12 is used for placing the blank paper P. After an inkjet printing operation is performed, the paper P is exited to the sheet output tray 13.
During the printing process of the inkjet printer 1, the blank paper P on the sheet input tray 12 is fed into the inkjet printer 1 in a feeding direction Y, and the transmission mechanism 11 is moved in a printing direction X. The printing direction X is perpendicular to the feeding direction Y. After the inkjet printing operation is completed, the paper P is exited to the sheet output tray 13.
Moreover, the internal components within the inkjet printer 1 comprise a sheet pick-up shaft (not shown), a sheet transfer shaft (not shown), a sheet ejecting shaft (not shown), . . . , and so on. By these internal components, the blank paper P could be transported from the sheet input tray 12 to the sheet output tray 13. For operating the internal components, the inkjet printer needs to provide the driving force to the internal components. Conventionally, the inkjet printer has several motors for respectively providing driving forces to the internal components for performing the printing purpose. The uses of too many motors are not cost-effective. For reducing the fabricating cost, an inkjet printer having a clutch mechanism has been disclosed. This clutch mechanism uses a single motor to transmit the driving force to many components. In other words, the clutch mechanism could transmit the driving forces to specified components according to the practical requirements. As such, the applications of the inkjet printer 1 are expanded. For example, since the use of a single motor could change the rotating speed of the sheet pick-up shaft, the papers P with different materials could be smoothly fed into the internal portion of the inkjet printer 1 from the sheet input tray 12.
For example, U.S. Pat. No. 5,841,450 disclosed a clutch-type power switching mechanism of an inkjet printer. FIG. 2 is a schematic view illustrating a power switching structure disclosed in U.S. Pat. No. 5,841,450. The power switching mechanism 2 is used for delivering the driving force of a motor 3 to a sheet pick-up module 4 including a sheet transfer shaft 41 and a feeding gear 42, or delivering the driving force to an ink cartridge purge module 5. The motor 3 is coaxial with a motor gear 6. The motor 3 provides a driving force to the motor gear 6 to drive rotation of the motor gear 6. The sheet transfer shaft 41 is coaxial with the feeding gear 42, and the sheet transfer shaft 41 is rotated with the feeding gear 42. The ink cartridge purge module 5 comprises a pump (not shown) and a pump gear 51. As the pump gear 51 is rotated, the pump is driven to carry out a purge operation so as to purge the ink cartridge.
The power switching mechanism 2 further comprises an idle kicker 21, a clutch gear set 22, a clutch shaft 23 and a spring 24. The clutch gear set 22 is sheathed around the clutch shaft 23. The clutch gear set 22 comprises a first gear 221, a second gear 222 and a third gear 223. The spring 24 provides an elastic force to the clutch gear set 22 for urging the clutch gear set 22 to move along the clutch shaft 23 in a direction A. The idle kicker 21 provides a pushing force to the clutch gear set 22 for driving the clutch gear set 22 to move along the clutch shaft 23 in a direction B. The motor gear 6 and the second gear 222 are engaged with each other at all times, and thus the clutch gear set 22 is continuously rotated with the motor gear 6. In a case that the clutch gear set 22 is moved along the clutch shaft 23 in the direction B, the third gear 223 is engaged with the feeding gear 42 to drive rotation of the feeding gear 42, and thus the sheet transfer shaft 41 is rotated. Whereas, in a case that the clutch gear set 22 is moved along the clutch shaft 23 in the direction A, the first gear 221 is engaged with the pump gear 51 to drive rotation of the pump gear 51, and thus the ink cartridge purge module 5 is enabled.
Although the above clutch-type power switching mechanism is able to transmit the driving force of the motor 3 to the sheet pick-up module 4 or the ink cartridge purge module 5, there are still some drawbacks. For example, since the clutch gear set 22 and the motor gear 6 for transmitting the driving force are non-coaxially but radially engaged with each other, the gap error resulted from the process of fabricating the inkjet printer may deteriorate the transmission stability between the gears. In this situation, undesired noise is generated.